The present invention relates to a parallax barrier device for permitting different images or an identical image to be viewed from a plurality of view points without the need for special glasses and to a method for fabricating the device. The present invention also relates to a display apparatus including a parallax barrier device.
To display three-dimensional images without using glasses, various methods have been proposed to date. As one of such methods, a lenticular lens method is known. A lenticule is a segment including a large number of small lenses and is used to control the traveling direction of light such that a right-eye image reaches the right eye and a left-eye image reaches the left eye. However, in general, the lenticular lens method has the drawback of incapability of switching between a three-dimensional image and a two-dimensional image.
As another method for displaying a three-dimensional image, a parallax barrier method has been proposed. In this method, light-shielding slits in the shape of narrow strips called barrier strips are used. For example, a right-eye image in the form of strips and a left-eye image in the form of strips are alternately displayed at a distance from the rear of light-shielding slits so that these images are seen through the light-shielding slits in such a manner that the viewer's right eye sees only the right-eye image and the viewer's left eye sees only the left-eye image. In this manner, a stereoscopic image is seen without the need for glasses. In such a method, a light-shielding part serving as a barrier and a light-transmitting part are fixed. Accordingly, when a viewer sees a two-dimensional image, the light-shielding part becomes an obstacle, resulting in the problem that a bright two-dimensional image is not obtained.
In Japanese Patent Publication No. 5-122733, disclosed is a method in which a three-dimensional image is displayed on a liquid crystal display panel and a barrier strip image is electronically generated by using another liquid crystal display panel so that stereoscopic vision of the three-dimensional image is produced. According to this method, in the case of displaying a two-dimensional image, the barrier strip image is erased so that the barrier strip image does not act as an obstacle. In this manner, a bright and clear two-dimensional image is displayed and the display can be switched between a three-dimensional image and a two-dimensional image. In such a technique, the shape of a transparent electrode on a liquid crystal display panel for displaying a barrier strip image needs to be patterned according to the shape of barrier strips. In particular, the patterning of the transparent electrode needs to be performed by etching, for example. Accordingly, in forming a fine electrode pattern, there might arise a problem in which a break occurs in wiring and the yield decreases.
In Japanese Patent Publication No. 8-76110, disclosed is a method in which a liquid crystal panel and a patterned polarizer are combined to create barrier strips so that stereoscopic vision of an image is produced. FIG. 7 is a cross-sectional view schematically showing a three-dimensional image display apparatus disclosed in Japanese Patent Publication No. 8-76110. The three-dimensional image display apparatus disclosed in Japanese Patent Publication No. 8-76110 will be described with reference to FIG. 7.
A liquid crystal panel 10B for creating barrier strips is provided at the front of an image display means 20B including pixel parts 101 constituting a right-eye image and pixel parts 102 constituting a left-eye image. A liquid crystal layer 33 is sandwiched and held between substrates 31 and 32 made of, for example, glass. A polarizer 34 is provided between the lower substrate 32 and the image display means 20B.
A patterned polarizer 30B is provided on the upper face of the upper substrate 31. The polarizer 30B includes a polarizing film 50 made of polyvinyl alcohol (hereinafter, referred to as a “PVA film”) divided into polarizing regions 51 having a polarizing function and non-polarizing regions 52 having no polarizing function. The PVA film 50 is sandwiched and held in a transparent supporter 60 made of, for example, triacetylcellulose (hereinafter, referred to as “TAC”) or glass. In this manner, the patterned polarizer 30B is formed.
FIG. 8 is a cross-sectional view showing a principle of a three-dimensional image display by the three-dimensional image display apparatus disclosed in Japanese Patent Publication No. 8-76110. The principle of a three-dimensional image display will be described with reference to FIG. 8. The apparatus is set such that the polarization direction of the polarizer 34 is orthogonal to the polarization direction in the polarizing regions 51 of the polarizer 30B. When a voltage is applied to the liquid crystal panel 10B to make liquid crystal molecules in the liquid crystal layer 33 stand, the polarizing regions 51 serve as barriers. On the other hand, the non-polarizing regions 52 transmit light, irrespective of the polarization direction. In this manner, the polarizing regions 51 are configured to serve as a parallax barrier with respect to the pixel parts 101 and 102, so that a three-dimensional image is displayed by a parallax barrier method.
FIG. 9 is a cross-sectional view showing a principle of a two-dimensional display by the three-dimensional image display apparatus disclosed in Japanese Patent Publication No. 8-76110. The principle of a two-dimensional image display will be described with reference to FIG. 9. When no voltage is applied to the liquid crystal panel 10B, the polarizing regions 52 are in the state of permitting transmission of light. Accordingly, the polarizing regions 52 do not become barriers, so that light passes through the entire surface of the liquid crystal panel 10B. In this state, if an image displayed by the pixel parts 101 and 102 is set as a two-dimensional image, the two-dimensional image is observed.
With the technique disclosed in Japanese Patent Publication No. 8-76110, even if a fine barrier strip pattern is used, patterning of the polarizer 30B eliminates the necessity of etching of an electrode pattern. Accordingly, a complex barrier strip pattern is formed without occurrence of wiring failure, thus providing a stereoscopic image display apparatus capable of electrically switching display between a two-dimensional image and a three-dimensional image.
However, the polarizer 30B disclosed in Japanese Patent Publication No. 8-76110 has the following drawbacks in fabrication. A process of fabricating the polarizer 30B will be described. A stretched PVA film 50 is attached to a transparent supporter 60 made of, for example, glass or TAC, and then a resist film is formed on the PVA film 50. A part 52 which is not to be provided with a polarizing function is masked, and then an exposed part 51 of the PVA film 50 is colored with iodine or dichromatic dye for providing a polarizing function.
An organic macromolecule (resin) film, particularly the PVA film 50 used as a polarizing film, is susceptible to expansion and shrinkage by heat or moisture and greatly varies in size, as compared to inorganic materials such as glass. Accordingly, not only in a case where PVA is attached to a substrate of an organic macromolecule material such as TAC with an adhesive interposed therebetween but also in a case where PVA is attached to a glass substrate exhibiting a small size variation, size variation due to lateral shearing of an adhesive layer might occur.
In a case where a resist pattern is formed on a PVA film by photolithography, a process of peeling off a resist with a solvent such as a caustic soda aqueous solution or a heating process such as pre-baking of a resist is needed. Therefore, the finished size of an actual resist pattern readily changes as compared to the design size of a resist (barrier) pattern, so that a deviation from the design size of a barrier pattern occurs. In addition, the polarizer 30B in which a barrier strip pattern is formed, the liquid crystal panel 10B and the image display means 20B for displaying images for the left and right eyes need to be placed at predetermined positions with accuracy. Accordingly, a higher positioning accuracy is required as the pattern of barrier strips becomes finer.
If the PVA film 50 exhibiting a large size variation as described above is patterned, the finished size deviates from the design size because of the large size variation. Accordingly, the accuracy in the size of the barrier strip pattern decreases and, in addition, the matching accuracy between the barrier strip pattern and an image display pixel pattern also decreases. As a result, the problem of harmful effects on a 3D image display arises.
To color the PVA film 50 patterned using a resist with iodine or dichromatic dye, new processes which have never been used in conventional processes of fabricating liquid crystal display apparatuses need to be introduced. This causes another problem of complicated fabrication.